Technological Field
The present invention relates to an image display viewing system and an image display device.
Description of the Related Art
Recently, a technology such as that described in Japanese Patent No. 3701355, for example, has become known that displays a plurality of video images on a single screen in a time-divided manner and that uses a pair of glasses with shutters that are synchronized to the timing of the displayed images in order to separate the plurality of the video images and recognize them individually. A technology such as that described in Japanese Patent Application Publication No. JP-A-61-227498 is also known that makes it possible to create a stereoscopic display by utilizing the aforementioned technology to display parallax images that respectively correspond to the left and right eyes.
These two technologies are substantially the same in terms of hardware, and they differ only in the video content they display and the operating of the shutters. That is, if the shutters that respectively correspond to the left and right eyes open and close in the same phase, the plurality of the video images can be selectively displayed, and if the shutters open and close in opposite phases, such that the two images serve as parallax images, the stereoscopic image can be displayed.
Incidentally, the vertical synchronization frequency of a television receiver is 60 Hz in the case of the NTSC system and 50 Hz in the case of the PAL and SECAM systems. Therefore, the pair of glasses with the shutters performs its opening and closing operations in synchronization at one of 60 Hz and 50 Hz.
At the same time, the frequencies of commercial power supplies that are used for external light sources such as an indoor fluorescent lamps and the like, for example, are the same 50 Hz and 60 Hz, and fluorescent lamps that are not of the inverter type flicker at double those frequencies, that is, 100 Hz and 120 Hz.
In a case where a fluorescent lamp and the pair of glasses with the shutters are used individually, the frequency is so high that the human eye does not perceive it, but if the fluorescent lamp is seen over the tops of the shutters, a flickering is perceived due to the difference in frequency between the operating frequency of the shutters and the flicker frequency of the fluorescent lamp. For example, in a case where a 60 Hz video signal is watched in an environment where the commercial frequency is 50 Hz, the flickering of the light is transmitted through the shutters at a frequency of one of 20 Hz and 40 Hz, which is the difference between the two frequencies, and is visually perceived. In this case, even if no flickering of the display screen itself is perceived, flickering is easily perceived in the area around the screen, such as on a wall that is illuminated by a fluorescent lamp, for example, and this will sometimes make a user feel uncomfortable.